Abstract Pancreatic cancer is a devastating disease characterized by the progressive accumulation of genetic mutations resulting in an untreatable condition. Pancreatic cancer is the eighth leading cause of cancer death worldwide and it is the fourth leading cause of cancer deaths in USA. Nearly 30,000 deaths each year in the United States are due to pancreatic cancer. The prognosis for pancreatic cancer is extremely poor with less than 5% of diagnosed patients surviving for 5 years due to the aggressiveness of the disease and the lack of effective therapies. Even combination therapy, such as surgery with radiation and chemotherapy, has not significantly improved the survival rate for patients with pancreatic cancer. Therefore, novel therapeutic strategies are required to treat this aggressive malignancy. Dysregulation of signaling pathways, including glycogen synthase kinase-3 (GSK-3), may lead to uncontrolled cell growth and hence tumor development. Thus, manipulation of these various cellular signaling pathways may be a potential therapeutic target. In this proposal, we plan to investigate the isoform specific growth inhibition and the mechanism of growth suppression utilizing shRNA against GSK-3 isoforms and small molecule inhibitors. In our preliminary studies, pancreatic cancer cells treated with GSK-3 inhibitor showed growth suppression which is associated with a significant reduction in active Notch1 and Notch3 proteins. Given the importance of the various pathways impacted by Notch, it is possible that Notch may be positively regulated by GSK-3. Thus, we hypothesize that Notch1 and/or Notch3 is most likely a key downstream target of GSK-3 inhibition in pancreatic cancer cells. In order to validate the effects seen in in vitro studies on pancreatic cancer cell lines with small molecule inhibitors, we will develop a xenograft model of tumor progression using GSK-3 isoform knock-out human pancreatic cancer cell lines. Since the activations and regulations of GSK-3 and GSK-3 have not been well established, the results from this proposal will determine the functional role of GSK-3 isoforms in regulating Notch.